Referring to FIG. 1 for a prior art driving and control circuit structure for controlling a backlight component of a display device (such as a liquid crystal display device), an alternate current (AC) from a power terminal 10 is filtered and rectified and supplied to two parts respectively. The first part is provided for driving the operation of a load which is a light emitting component such as a cold cathode fluorescent lamp (CCFL), and the second part is provided for supplying electric power to a control circuit such as a control circuit board or an AD board.
The circuit structure of the first part comprises: a first power factor correction unit 11 connected to a power terminal 10 for correcting the power factor of a power supply and outputting a DC power (a middle-voltage DC power approximately equal to 380˜400V), and an inverter 12 (which usually includes a PWM control circuit and an inverter for converting the middle-voltage DC power into a high-voltage power output and driving a backlight light emitting component 18 such as a cold cathode fluorescent lamp). The circuit structure of the second part comprises: a second power factor correction unit 13 connected to a power terminal 10 for correcting the power factor of a power supply, a DC/DC transformer unit 14 (which is usually an isolation transformer whose primary and secondary windings are separated from each other and not grounded jointly, and the primary winding of the DC transformer unit 14, the first power factor correction unit 11 and second power factor correction unit 13 are grounded together), and an AD board 15 installed at a secondary winding of the DC transformer unit 14 and coupled to an inverter 12 of the foregoing driver stage through an isolation optical coupler 16, 17 for controlling or correcting the inverter 12 and changing the operating status of a backlight light emitting component 18.
Since the prior art inverter 12 and the aforementioned first power factor correction unit 11 have the circuit structures that are grounded jointly (or grounded to a high-voltage power supply), and the AD board 15 and the inverter 12 are isolation circuit structures that are not grounded jointly. Therefore, a control signal (such as an ON/OFF control signal for controlling the ON/OFF of the backlight or dimming the brightness of the backlight) in the AD board 15 cannot be connected directly to the inverter 12, but it is necessary to use an isolation optical coupler 16, 17 to control the inverter 12 (such as dimming the backlight component and controlling the ON/OFF of the backlight component). Such method of using the isolation optical coupler 16, 17 to transmit control signals definitely will increase the number of optical couplers. On the other hand, since the power factor correctors (including the first power factor correction unit 11 and the second power factor correction unit 13) and the power terminal are grounded jointly, and the primary and secondary windings are not isolated from each other, it will jeopardize the safety of users.